The invention relates to processes for enhancing solubility and reaction rates of in supercritical fluids, and more particularly to such processes as they relate to the fabrication of semiconductor devices.
As the demand for ever-smaller silicon devices continues, and as resolution continues below the sub-micron level, the need for uniform and precise processes for depositing conductive pathways and interconnects is increasing. It is also desirable for such processes to proceed rapidly. For example, it is frequently desired to form metal-containing materials in and over semiconductor substrates. The metal-containing materials can be incorporated into integrated circuit devices, and/or can be utilized for formation of conductive interconnects between integrated circuit devices. There is also a need to provide substantially clean and defect free semiconductor substrates and surfaces onto which other materials may be deposited. Processes for uniformly and precisely etching and/or cleaning such substrates are needed.
Wai et al, U.S. Pat. No. 6,653,236, describe methods of forming metal containing films over surfaces of semiconductor substrates using a supercritical fluid that contains metal forming precursors dispersed therein. A supercritical fluid is a composition that exists in a quasi-liquid state above a defined critical pressure and a critical temperature for the composition. For example, carbon dioxide becomes a supercritical fluid at temperatures above 31° C. and pressures above 1073 psi (73 atmospheres). Typical working conditions for supercritical CO2 are in the range of from about 60-100° C. and 1500-4500 psi. The use of supercritical fluids permits much greater amounts of precursors and/or reactants to be dissolved or dispersed than prior CVD (chemical vapor deposition) processes. However, reaction rates have been slower than predicted.
Others have used ultrasound in attempts to enhance reaction rates on semiconductor substrates. For example, Hembree et al, U.S. Pat. No. 6,224,713, describe a method and apparatus that uses ultrasonic waves to wet etch silicon substrates to provide defect-free silicon structures. But, these methods have applied ultrasonic energy to traditional reactions carried out in conventional liquids. It is well known that the application of ultrasonic energy to conventional liquids causes cavitation and/or microbubble formation. It is these mechanisms that enhance mixing of reactants to increase reaction rates. However, cavitation and microbubble formation are not possible using supercritical fluids. By definition, cavitation and gas bubble formation cannot occur in a fluid maintained at or above its critical point.
Accordingly, the need still exists to enhance reaction rates in supercritical fluids and to enhance reaction rates on or in semiconductor substrates. The need also exists for processes that produce uniform and precise results in the deposition or removal of materials from the surfaces of semiconductor substrates.